This invention relates to an improvement of a starting device which activates a seat belt tightening device which, upon collision of the vehicle, rotates the winding shaft of its retractor, or an air bag device which, upon collision off the vehicle, inflates its air bag with gas to protect the passenger from being shocked by the collision.
Recently, in an emergency such as the collision of a vehicle, in order to protect passengers in the vehicle, passive constraining means such as a seat belt tightening device and an air bag device have been extensively employed.
The seat belt tightening device is designed for instance as follows: A piston slidably set in a cylinder is coupled to one end of a cable wound on a pulley which is mounted on the winding shaft of a retractor. The pressure of expansion of the gas acting on the piston applies tension to the cable, so that the cable turns the winding shaft of the retractor in a webbing winding direction, thereby to tighten the webbing laid over the passenger. Therefore, the seat belt tightening device includes a gas generator which supplies the gas which, as was described above, acts on the piston in the cylinder to apply tension to the cable. The gas generator comprises an igniting heater, and explosive. In response to a detection signal from a collision sensor, the igniting heater is electrically energized to generate heat to ignite the explosive thereby to produce the gas which is applied to the piston.
The air bag device is designed for instance as follows: A module is set in the steering wheel, which is made up of a center pad, a folded air bag, and an inflator (or gas generator). Upon collision of the vehicle, the inflator is activated to generate gas quickly to inflate the air bag instantaneously. The air bag thus inflated receives the passenger and decreases the shock applied to him. For this purpose, the air bag device has a gas generator which produces gas to inflate the air bag. In the gas generator, and igniter (priming composition) is ignited to burn an explosive (propellant) to produce gas. The gas thus produced inflates the air bag.
Hence, it is necessary for the gas generators of the seat belt tightening device and the air bag device to have a starting device which, upon detection of the collision of the vehicle, burns the igniter (priming composition) to activate the gas generator. The starting device is generally designed as follows: Similarly to the igniting devices disclosed by Unexamined Japanese Patent Publication Nos: Hei. 2-24242(1990) and Hei. 3-96456(1991), an igniting heater is provided for the igniter (priming composition), and it is electrically energized to generate heat to burn the igniter (priming composition).
The starting device needs a vehicle body acceleration detecting means, such as a sensor for sensing the collision of a vehicle or the like, to produce an igniting signal. The starting device also needs a control circuit for determining, via from the igniting signal, whether or not the igniting heater should be electrically energized. Therefore, the number of components of the starting device are relatively large and intricate in structure. Furthermore, in order to assure the reliability of the starting device, it is essential to positively connect the various component means to one another. That is, it is rather difficult to assemble the starting device with high efficiency, and accordingly the resultant starting device is expensive.
In order a starting device to overcome the above-described difficulties has been proposed by Unexamined Japanese Patent Publication No. Hei. 4-108049 (1992). In the starting device, upon collision of the vehicle, a weight, which serves as a vehicle body acceleration sensor, causes an igniting pin to strike a detonator provided for the igniter (priming composition), in order to burn the igniter (priming composition). However, this starting device is a mechanical one which operates without an intricate control circuit.
More specifically, in the starting device, when the weight moves, the trigger shaft is turned, so that the stopper of the latter is disengaged from the flange of the igniting pin. Consequently the igniting pin is pushed out by the elastic force of a compression spring to strike the detonator.
In the case of the above-described starting device in which the igniting pin is caused to strike the detonator in the igniter (priming composition), the engaging portions of the stopper of the trigger shaft and the flange of the igniting pin may rust or may be fixedly tied to each other when it is used for a long time. In addition, it is rather difficult to stabilize the frictional coefficient of the engaging portions. The weight, which is the vehicle body acceleration detecting means, is vibrated not only when the vehicle collides with something but also when the door is closed or when the vehicle body is knocked. Therefore, if the sensitivity of the weight is carelessly increased, then the probability is increased that the starting device will operate erroneously. Consequently, it is difficult to adjust the acceleration detecting characteristic of the starting device. Thus, designing the starting device must be extremely precise.